Although widespread use of combination antiretroviral therapy (cART) has effectively increased the life span of many infected individuals, HIV-1 continues to be a major public health issue in both developed and poor resource settings. As such, understanding the basic mechanisms of its replication cycle is instrumental to the development of new approaches to treat infection. HIV-1 employs unusual, intricately intertwined early infection strategies involving reverse transcription, disassembly of capsid core (also known as ?uncoating?) and transport to the nucleus. Although its precise timing and location remain contentious, growing evidence suggests that at least partial uncoating occurs in the cytoplasm during transport to the nucleus. Indeed, incoming HIV-1 particles exhibit microtubule (MT) based bi-directional motility suggestive of their association with both inward (dynein) and outward (kinesin) MT motors, and recent studies suggest that the opposing forces generated by these motors facilitate uncoating. Despite this, HIV-1 does not appear to bind motors directly but instead, uses motor adaptors whose identity remained enigmatic until recent years. Our work funded in the previous cycle identified the HIV-1 kinesin-1 adaptor as Fasiculation and Elongation Factor Zeta 1 (FEZ1). We further established FEZ1?s central role in the transport and uncoating of incoming viral particles in natural target cells, which is regulated through FEZ1 phosphorylation that controls kinesin-1 activity. Moreover, we found that HIV-1 cores bind microtubule associated regulatory kinase 2 (MARK2) to locally control FEZ1 phosphorylation on viral particles. We further showed that HIV-1 particles also bind highly specialized MT regulatory proteins to induce the formation of stable MT networks, a subset of MT filaments favored by kinesin motors. Using innovative structural and functional studies in collaboration with the Xiong Lab at Yale University, our preliminary data reveals an usual and high affinity binding strategy used by HIV-1 to engage FEZ1 for transport that is mediated by capsid hexamers and one of four coiled-coil domains in FEZ1. Data also suggests that FEZ1 and MARK2 compete for binding in a manner that controls the extent of FEZ1 phosphorylation on HIV-1 capsids. In addition, we identify a new host factor that our data suggests binds distinct coiled-coil regions in FEZ1 and is exploited by incoming viral particles to enhance MT stabilization at the cell periphery. Cumulatively, our data suggests that distinct coiled-coil domains in FEZ1 mediate capsid binding, motor recruitment and MT stabilization to coordinate several aspects of early HIV-1 transport and uncoating. In this proposal, we aim to determine how FEZ1 and MARK2 function on the HIV-1 capsid to promote early infection and expand upon our new findings that FEZ1 plays a multifunctional role in early infection by recruiting both motors and regulators of MT stability to incoming HIV-1 particles. The outcome of our studies will provide important mechanistic insights into the multifunctionality of FEZ1 and expand our broader understanding of how HIV-1 controls several important steps in early infection of natural target cells.